Machine gun



1948- G. A. CHADWICK ETAL 2,453,3@

MACHINE GUN l5 Sheets-Sheet 1 Filed Dec. 21, 1932 IM A G- A QHAWICK I5 MACHINE GUN l5 Sheets-Sheet 2 Filed D60, 21, 1932 /IV/////////I//I// lI/J I G. A. CHADWECK ETAL, MACHINE GUN Filegi Dec. 21, 1932 Wm, M, i G. A. QHADWICK HAL 3 MACHINE GUN l5 Sheets-Sheet 5 Filed Dec. 21, 1932 g g g MACHINE GUN l5 Sheets-Sheet 6 Filed Dec. 21, 1932 l5 Sheets-Sheet 7 MACHINE GUN L .A K w W m H c A G Filed Dec. 21, 1932 Nov. 1 6, 1 48.

e. A. CHADWICK ETAL.

MACHINE GUN l5 Sheets-Sheet 9 Filed Dec. 21, 1932 1s Sheets-Shet 10 G. A. CHADWICK HAL. MACHINE GUN NW. 1, E94.

Filed Dec. 21, 1932 av. 16, 194. G. A. CHADWICK ETAL 2,453,830

MACHINE GUN Filed Dec. 21, 1932 15 Sheets-Sheet ll W w\ v 3 H H v w Q Q o W wQ Mki L m L MD Nam 16, 1948. e. A. CHADWICK- ETAL MACHINE GUN l5 Sheets-Sheet 12 Filed Dec. 21, 1932 W W 2 QWW II .I

H M A/ mm I 236 fiwerdbrs:

@eorge d. UMEa/LZE aflbrlwy Paul Z29- 360% In A k m w D A H c A momma mm 15 Sheets-Sheet l4 Filed Dec. 21, 1932 im A K m w D A H c A G MACHINE GUN l5 Sheets-Sheet 15 Filed Dec. 21, 1932 Patented Nov. 16, 1948 MACHINE GUN George A. Chadwick and Paul W. Burk, Washington, D. C.

Application December 21, 1932, Serial No. 648,296

This invention relates to a machine gun and has for its numerous objects the general improvement of the eifectiveness and safety of this type of weapon. The several objects will more fully appear from the description of the construction and operation of our invention.

In the drawings:

Fig. 1 is a side elevation of the assembled gun;

Fig. 2 is a partial longitudinal section showing the water jacket and recoil spring;

Fig. 3 is a detail view showing a cartridge in the feed plate ready to be forced into the chamber;

Fig. 4 is a partial longitudinal section showin the recoil actuated breech operating mechanism;

Fig. 5 is a sectional detail of a relief valve in the hydraulic breech operating mechanism;

Fig. 6 is a partial longitudinal section through the breech mechanism;

22 Claims. (Cl. 89-490) Fig.7 is a partial transverse section on line 1-4 of Fig. 6;

Fig. 8 is a sectional detail of the plunger mechanism on line 8-8 of Fig. 18;

Fig. 9 is a transverse section showing the breech block and breech locking mechanism in the closed position;

Fig. 10 is a fragmentary view of the same parts as shown in Fig. 9 with the breech block unlocked;

Fig. 11 is a partial longitudinal section through an empty magazine in position above the loading plate taken on line H--ll of Fig. 25;

Fig. 12 is a longitudinal section of the rear portion of the gun slide showing the buffer mechanism for stopping the carrier;

Fig. 13 is a detail View of the extractor lifting cams;

Fig. 14 is a transverse section of the rear end of the slide showing the breech housing moved back;

Fig. 15 is across sectional view through the car rier and breech block on line l5l5 of Fig. 6;

Fig. 16 is a view similar to Fig. 15 but taken on line l6'-|6 of Fig. 6;

Fig. 17 is a cross section through the barrel and the hydraulic recoil mechanism on line |Ill of Fig. 4; v

Fig. 18 is a view similar to Fig. 17 taken on line 18-18 of Fig. 4;

Fig. 19 is a face elevation of the breech end of the gun;

Fig. 20 is a side elevation of the parts shown in Fig. 19;

Fig. 21 is a cross section on line 2l2l of Fig.

of the gun in such a position that the breech is open;

Fig. 22 is an elevational detail view of the carrier locking mechanism and the trigger assembly;

Fig. 23 is a detail view of a part of the hand cocking mechanism;

Fig. 24 is a detail view of a means for manually moving the carrier rearwardly;

Fig. 25 is a cross section through an empty magazine and a loaded magazine in position in the cradle taken on line 25--25 of Fig. 11;

Fig. 26 shows a cartridge in the lower part of a. magazine in the position indicated by line 2626 of Fig. 27;

Fig. 27 is a view of a loaded magazine with one side thereof removed;

Figs. 28 and 29 show details of the means for supporting the noses of the cartridges in the magazine;

Figs. 30, 31 and 32 are respectively top plan view,

longitudinal section and rear end view of the carrier;

Figs. 33, 34, 35 and 36 are details of the breech locking wedges;

Figs. 37, 38 and 39 are respectively a longitudinal section, a side elevation and a front elevation of the breech block;

Figs. 40 and 41 are respectively longitudinal section and front end elevation of the extractor;

12 showing the mechanism to prevent operation of the gun in the event of failure to extract a spent case from thechamber and to stop the operation Fig. 42 is a top plan view of the breech housing with parts in section;

Fig. 43 is a side elevation of the breech housing;

Fig. 44 is a cross section of the breech housing on line 44-44 of Fig. 42;

Fig. 45 is a cross section on line '4 5-45 of Fig. 43.

This gun is composed of the following main parts or assemblies: A slide 46, a gun barrel 41, a magazine cradle assembly 48, a breech mechanism, a feed plate, a recoil and breech operating system, and a cooling system.

The slide 46 is preferably a bronze casting and serves as a foundation upon which the rest of the gun is built. Upon the rear end of the slide is mounted the rear plate 49. Adjacent the forward end is formed an expansion chamber 50 for the oil used in the hydraulic recoil system. Trunnions 5| serve to mount the gun pivotally in any suitable supporting means adjacent which are pads 5| for securing an elevating arc to the gun. The forward bracket 52 and rear bracket 53 support the magazine cradle 48. The forward end 54 of the slide is contracted to serve as the forward bearing in which the gun barrel slides and is externally threaded at 55 to provide means for securing the water jacket 56 thereto. An oil cup 3 51 supplies lubricant to the forward bearing. Just forward of the bracket 52 the slide is thickened to form the rear bearing and has a shoulder 68 formed thereon to act as the stop for the forward movement of the barrel, lubricant for the rear bearing being fed from cup 59. In the slide slot 85 in position to be engaged by a cartridge passing into the slot. At the rear face of feed plate 82 a feed sear 92 is secured to shaft 98 and there is provided a packing gland 58 to prevent leakage of the. cooling water which is introduced through the hole 6| and withdrawn through outlet 62, it being the intention to circulate running water to cool the gun. Recoil cylinder 228 is secured to the lower side of the slide between the rear bearing and expansion chamber 58, while the forward end of the slide is extended downwardly to form a pocket 64 for the recoil yoke, access thereto being had by removing plate 65. On the under side of the gun below the chamber 58 is a shoulder 66 that is the stop for the rearward movement of the barrel; it is engaged by the rear side of the yoke if the brake mechanism does not theretofore stop the recoil movement.

The gun barrel 41 is a single tube having a chamber 61 at its rear end to receive the cartridge.

Breech housing 68 is secured to the barrel by an internal nut 69 screwed into the forward end of the breech housing and bearing against shoulder 18 on the barrel to draw shoulder 1 I on the breech housing against packing 12 that is disposed between shoulder II and rib 13 on the barrel to prevent leakage of the cooling water which enters through hole 6| and flows around the barrel in space 14 from which it passes through opening 15. Forward of the breech housing, the barrel 41 is externally threaded to receive a nut 16 that clamps the recoil yoke l1 against shoulder I8 on the barrel. Some distance forward of the yoke 'I'I, barrel 4'! is externally threaded to receive a nut I9 that confines recoil spring 88 under the desired degree of compression against the front end of the slide. The front end of water jacket 56 is closed against leakage by a gland 8| secured inthe end of jacket 56.

Cartridges are received from the magazine by feed plate 82 that is fixed to the slide between brackets 52 and 53. This plate is provided with transverse ribs 83 and 84 against which the bottom cartridge in a magazine will bear, the latter rib being higher than the former to support the smaller end of the cartridge. The upper faces of these ribs are arouate with their centers of curvature on the opposite sides of a vertical axial plane through the gun so that the pressure of cartridges against the ribs will produce a component tending to swing the magazine toward the median longitudinal slot 85 through which the cartridges pass to be rammed into the chamber. Grooves 86 lead downwardly from the rear end of slot 85 to guide the rim of the cartridge case into alignmentwith the chamber; the slot 85 is narrowed forwardly to form a downwardly sloping cam surface 81 facing rearwardly and downwardly at each side of the slot 85 to engage the sharply tapered portion 'of the cartridge to guide the nose thereof to chamber 61. Spring pressed plungers 88 support the nose of the cartridge in the feed plate, these plungers having suitably beveled faces to engage the sloping surface of the bullet and a beveled projection 89 to extend partially thereunder. The lower faces of the plungers 88 contact sloping faces on the feed plate 82 to prevent their being moved away from the cartridge by the weight thereof or by the pressure of the magazine springs. A shaft 98 is rotatably mounted in the rear end of feed plate 82 and has secured to it a detent 9i that extends out into is connected to spring 93 under tension that tends always to move the detent 9I into slot 85. Rear stop lever 94 has offset arms 95 and 96, the latter being disposed under the free end of feed sear 92 except when the detent 9I Is moved out of slot by a cartridge.

Stop sear 91 is plvotally mounted on the slide with its free end movable under the end of arm of the rear stop lever, but normally held out of that position by a spring pressed plunger 98 that acts upon carrier locking rod I51 connected to the stop sear. Upon the rear stop lever is a surface 99 against which the extractor contacts and since the rear stop lever cannot be rotated unless detent 9| is moved out of slot 85 by a cartridge, and also unless stop sear 91 is clear of arm 95 of rear stop lever 94, the carrier will be held and the operation of the gun will be stopped, as will be hereinafter more fully explained.

The breech mechanism takes the cartridge from fe'ed plate 83, rams it into the gun chamber 61, closes the breech, fires the charge, opens the breech, extracts and ejects the empty case. It consists of the breech housing, carrier, breech block, firing mechanism, rear stop lock, antidouble loader, and carrier buffer.

The breach housing 68 is a steel forging connected to the barrel as above set forth in connection with the description of the barrel. The forward end of the breech housing is bored out to receive the chamber end of the barrel and has formed in it the space 14 for the circulation of cooling water. The outer surface of the forward end of the breech'housing slides in the rear bearing and the front end thereof 'contacts shoulder 68 to stop forward movement of the barrel. A short distance from the back face of the barrel the breech housing is divided into two side members I88 and IM that extend almost to rear plate 49' where they are connected together by a bridge I82 that carries an internally threaded lug I83 adapted to be .engaged by a threaded rod to pull the breech housing backwardly for testing the gun. In the inner face of members I 88 and IM are, formed grooves I84 to engage the rim of the cartridge case and guide the case along the axis of the gun into the chamber, these grooves being connected to grooves 86 in the feed plate by an inclined portion I85. A curved groove I86 in each of members I88 and I8I connects with grooves I84 in the sanie member, respectively, and guides the spent casedownwardly-and out of the gun. A dowel pin I87 serves to position the barrel properly in the breech housing and a key I88 disposed in groove I89 in the housing and groove H8 in the slide prevents rotation of the housing and barrel with respect to the slide, but permits relative longitudinal movement between these parts. A short distance from the rear face of barrel 4! a block III is set in each side of the passage through the breech housing; each-of these blocks has an outwardly sloping face H2 to coact with a face on a locking wedge H8. A short distance forward of the rear ends of members I88 and IM there is disposed in each of these members an extractor-lifting'cam II4, each cam being pivotally mounted at one end and urged toward the space between members I88 and MI by a U-shaped spring II5, as shown in Fig. 13. Each of these cams has a rearwardly sloping face II6 to permit the extractor to ride up over the cams when the breech mechanism is being moved forwardly.

The member IIII carries at its rear end a downwardly extending cam II1 for automatically cocking the firing mechanism.

Grooves IIB are formed in the inner faces of members IIII in which grooves the carrier H9 is slidably mounted. As shown in Figs. 30 to 32 inclusive, the carrier has in it a longitudinally extending bore I20 in which the firing pin I2I is slidable, the rear portion of this bore being of greater diameter to receive the enlarged rear portion of the firing pin in which firing pin spring I22 is held in operative position by the spring retainer I23 secured to the carrier by pin I24, Locking wedges II3 have elongated holes I25 in their limbs I26 to receive a pin I21 that is seated in a hole I28 in the carrier, which pin is bored to permit the firing pin to be passed therethrough, the elongation of the hole permitting the locking wedges to slide as well as pivot on pin I21, the limbs of each locking wedge being placed astride the portion I29 of the carrier. The front end of portion I29 has on it oppositely sloping faces I30 fall to function.

The locking wedges II3 (Figs. 33-36) each have two limbs I26 adapted to embrace the portion I29 of carrier II9, the limbs of one of the Wedges being sufficiently spaced apart to lie outside the limbs of the other wedge. Upon the upper and lower surface of each wedge H3 at its forward end is a lug I34 having a rounded rearward face, which lugs are adapted to seat in grooves I35 in the breech block, the grooves I35 being formed to define a very obtuse angle opening forwardly, the front edges of the grooves having somewhat the same angular relation to each other as do faces I 36 on the breech block that are engaged by the locking wedges when ramming a cartridge into the chamber. Upon rearward movement of the carrier after firing, pin I21 pulls back on the wedges and lugs I34 engage the rear faces of slots I35 and thereby draw the locking Wedges backward, the inward slope of the rearward faces of the. groove moving the locking wedges in so they will clear the blocks H2 and permit the breech block to be unseated. A beveled surface I31 on the rear inner face of each locking wedge provides an appreciable contact area against which portion I29 bears to lock the wedges positively in the closed position. The inner face of each wedge II3 has in it a groove I38, semi-circular in cross section, to provide clearance for the firing pin.

Adjacent the forward end of breech block I32 is a groove I39 that extends across and down each side of the breech block to receive extractor I40. As shown in Figs. 40 and 41, the extractor is a substantially horseshoe-shaped member having legs to engage in the slot I39 on the sides of the breech block and a forwardly projecting portion I4I with a backwardly sloping beveled face I42 on its lower edge and a slot I43 back of that edge, the beveled face I42 being adapted to engage the rim of a cartridge case to cause the extractor to ride up over the rim and thus set the rim in slot I43 whereby backward movement of the 6 breech mechanism will withdraw the spent case from the chamber. A backwardly sloping face I44 is formed on the forward edge of each leg of the extractor at the lower end thereof to cause the extractor to slide over extractor cams II4 as the breech mechanism is being moved forwardly to ram a new cartridge. Two extractor springs I45 have their rear ends bent over and engaged in a slot I46 in the upper rear portion of the breech block and extend forwardly to lie upon the upper face I41 of the extractor to move the extractor downwardly upon the breech block and yet permit it to rise sufficiently to pass the rim of a. cartridge case. Breech block I32 has in it a passage I48 for the firing pin, and leading downwardly from that passage a small opening I49 to permit the escape of gases that may enter the passage I48 from a ruptured primer and also to permitany particles of carbon that may be carried by such gas into the passage I48 to drop from the passage and so prevent interference with the movements of the firing pin by such particles. In the lower portion of the forward end of breech block I32 is a forwardly and upwardly sloping slot I50 to accommodate one arm I52 of the anti-double loader lever I5I, which arm is adapted to be engaged by the rim of a cartridge case in the chamber thereby rocking shaft I53 and actuating a carrier locking mechanism hereinafter to be described to prevent a second cartridge being rammed while a case is still in the chamber. The arm I54 of lever I5I will catch the nose of a cartridge that may have dropped down unduly while being loaded and guide the same up into chamber 61. at the lower rear portion of chamber 61 to receive arm I52 of lever I5I when a cartridge case is in the chamber. The outer end of shaft I53 carries a lever I56 that engages a hook'on carrier looking rod I51 that is connected to stop sear 91 whereby, when arm I52 is held down by the rim of a cartridge case in the chamber and lever I56 is thereby rocked forwardly, the stop sear 91 is moved under arm of rear stop lever 94 and the rear stop lever cannot then rotate on its pivot so that when the face 99 of rear stop lever is contacted by extractor I49, the extractor is prevented from riding up over extractor cams I I4 and the mechanism is locked with the breech open. The position of lever I56 may be ascertained by looking through hole I56 in the slide and hence it can be determined whether failure to fire is due to hangfire or misfire or failure to ram a charge. and the case has been extracted, as in normal operation, stop 91 is held back by plunger 93 and the rear stop lever can be rotated by the extractor, thus permitting the extractor to move over the extractor cams and allow the breech mechanism to close. When it is desired to hold the breech open, carrier locking rod I51 may be held in the forward position, in which the stop sear 91 is under arm 95 of the rear stop lever, by moving plunger I58 downwardly through a loop I59 formed on the rear end of the carrier locking rod, or by pressing the thumb against loop I59. A hairpin-shaped spring I69 is provided to engage grooves I6I in plunger I58 to retain the plunger in either the locking or unlocking position.

From rear plate 49 a sleeve I62 extends outwardly, this sleeve having in it a passage in which a trigger rod I63 is slidable and having a slot in the lower part of its wall to permit slid A slot I55 is formed However, when the breech is open.

ing movement of trigger I64. Spring I65 is disposed around trigger rod I63 and is held under compression between a pin I66 fixed to rod I63 and the inner face of rear plate 49 to hold trigger rod I63 normally forwardly and also under rotational tension to exert a clockwise torque on triggcr rod I63. Opening into the right-hand side of the passage in which trigger I64 slides is a slot I64 having a forwardly extending portion. 'ihc sLop I68 prevents movement of bar I69 connected to rod I63 to the rear to the extent that bar I69 would be withdrawn from guide I10. Stop I63 is resilient and can be moved aside to permit the withdrawal of bar I69 from guide I10 .s disassembling. A cam surface "I on the inner face of bar I69 is engageable with a member I12 (Fig. 16) that bears against a collar I13 slidably mounted in the breech housing; a spring I14 is disposed around a plunger I15 between collar I13 and a fiange I16 on the plunger. A cam face I11 on the outer edge of bar I69 is adapted to contact a yoke I18 connected to the plunger to move the plunger outwardly when the breech is to be opened manually. To do this, trigger I64 must be turned counter clockwise and moved forward in slot I64. The delay in opening the breech thus occasioned is an added factor of safety in case of a hangfire. So long as plunger I15 is held inwardly, the breech cannot be opened. In automatic fire, as the barrel and breech housing are moved back by the recoil, the plunger I15 moves with them and thus the yoke I18 is made to ride over cam face I11 on member I69, which is carried by the slide and does not recoil, which withdraws the plunger I15 and permits the breech to be opened, as will hereinafter be explained.

Slidably mounted in carrier I I9, to be in alignment with plunger I 15 when the breech is closed, is a sear I19 that is urged toward the plunger I15 by a spring I80. Sear I19 has in its forward side a slot I8I in which arm I82 of sear lever I83 is slidable, the sear lever having in one face a cut-away portion to form a shoulder I84 with which the sear will be moved into engagement by spring I80 when the sear lever is rocked backwardly by pivot I85 that is mounted in opening I86 in the carrier. Arm I81 of scar lever I83 engages toe I88 of the firing pin I2I and thus draws back the firing pin and compresses firing pin spring I22 against spring retainer I23 when the sear lever is rocked backward. When trigger I64 is moved backwardly to bring cam face "I into the position with respect to plunger I15 shown in Fig. 7, spring I 14 is free to move plunger I15 toward sear I19 and disengage the sear from shoulder I84 on sear lever I83 which permits the spring I22 to drive the firing pinforward and fire the cartridge.

The gun is cocked, that is, sear lever I83 is rotated to retract the firing pin and compress the firing pin spring, by the portion I90 of cocking lever I9I being formed downwardly by automatic cocking cam II1 carried by member I of the breech housing. Lever I9I is connected to pivot I85 upon which sear lever I83 is keyed and thus the downward movement of this lever I9I r0 tates sear lever I83 backwardly which effects the cockin operation. Provision is made for recocking the gun by hand by means of a bar I92 mounted in a rod I93 that is slidable through rear plate 49 and has a hook I94 formed on its forward end to engage a lever I 95 carried by a shaft I65 to the other end of which is connected a lever I91 that may be brought into engagement with portion I90 of lever I9I to rock lever I9I backwardly. A spring pressed plunger I98 bears against a finger I 99 extending oppositely to lever I91 and connected thereto to retain lever I91 in contact with hook I94 on rod I93.

Ammunition is fed into the gun from magazines 200 mounted in cradle 48. The magazines are enclosed on all sides except that which is presented to the feed plate when mounted in the cradle. A plurality of leaf springs 20I connected together at their ends and substantially at their mid points are placed under compression when the magazine is loaded and force the cartridges out when feeding into the gun. A push plate 202 connected to the lowermost leaf has members 203 attached thereto to contact the cartridge case and a trip plate 204 at its forward end to release the cradle latch when the magazine is empty. At the lower edge of the forward end of each magazine 200 is a slot 205 into which the cradle latch 205 may pass to lock the cradle in position to align the cartridges in the magazine that is engaged by the cradle latch with slot 85 in the feed plate, the inner end of latch 205 extending a short distance into the magazine in position to be contacted by trip plate 204 when the magazine is empty. A pin 206 is fixed in latch 205 to facilitate manual movement of the latch. Each magazine is provided on each of its sides with a block 201 that fits in a recess in the face of bar 208 that extends lengthwise of the cradle at its upper side to support the magazine in the cradle, the springs 209 secured to the sides of the cradle serving to hold blocks 201 seated in the recess in bar 208 but yielding readily to facilitate placing the magazine in the cradle.

The rim ends of the cartridges are retained in the magazine by a spring clip 2I0 that has an overturned portion 2 which extends beneath the rim of the lowermost cartridge until the magazine is placed in cradle 48 at which time tabs I61 carried by portion 2 ride over cam members I61 in cradle 48 and move the overturned portion out of engagement with the cartridge rim to the position shown in Fig. 11. The noses of the cartridges are supported by spring clips 2I2 inside the magazine at the forward end thereof, each of which has its lower end inturned toward the cartridge. A plate 2I3 is slidably carried on the outside of the magazine and normally covers the aperture in the side of the magazine through which pins 2 I4 fixed to the clips 2I2 are adapted to pass (Fig. 26), the plates 2I3 being held in position to cover those apertures by springs 2I5 bearing thereon. However, when the magazine is placed in the cradle, the lower edge of each plate 2| 3 contacts a shoulder, 2l6 at the lower edge of the cradle and the plate is moved upwardly to align an aperture 2 I 1 in the plate with the corresponding pin 2I4 whereupon the action of the pressure of springs 20I against the cartridges forces clips 2I2 laterally and the cartridge may then move out of the magazine. The force exerted by the lowermost cartridge against ribs 83 and 84 due to springs 20I has a component directed toward the slot in said plate and therefore, as soon as cradle latch 205 is released by contact with the trip plate 204 in an empty magazine, the loaded magazine is caused to move into position above slot 85 in the feed plate where it is locked by latch 205 until it in turn has been emptied. This method of loading from the top of the gun and the ejection of the spent cases from the under side thereof permits placing several guns in a single mount if desired, which is not possible where the ammunition is fed through the sides as is the usual practice. So long as the empty magazines are replaced by loaded magazines and the gun continues in action, the cradle will be automatically swung back and forth to position the loaded magazines over the slot in the feed plate as soon as the previously used magazine is emptied.

The gun mechanism is operated by the recoil due to the discharge of the cartridge which moves barrel 41 back in slide 46 and comprises recoil spring 80, thus storing up energy to return the gun to battery. Yoke 11 is connected to the barrel and to piston rod 2|8 that carries piston 2i9 slidably mounted in recoil cylinder 220. Inside piston 2l9 is mounted a throttling tube 22l having in it a seat for valve 222 that closes the passage through the throttling tube at certain times and is normally held against its seat by spring 223 bearing against the valve stem 226 which is sli'dably mounted in piston rod 2I8. Valve 222 has a somewhat close fit in the forward portion of the throttling tube to restrict the passage of the liquid, which increases the pressure on the rearward face of piston 2l9 and results in a greater braking effect on the recoiling parts of the gun. Throttling rod 225 is mounted 'inthe rear end of recoil cylinder 220 and has threaded in it the valve stroke adjusting bolt 226 to hold valve 222 unseated for a predetermined time. Suitable stufling boxes 221 and 228 prevent leakage of oil or water around piston rod 2i8. The space in cylinder 220- in front of piston 2!!) is in communication with the passage through the throttling tube by a port 229. Expansion chamber is connected to cylinder 220 through passages 230, of which there is one on each side of the gun barrel, opening into the cylinder through port 23l. Each passage 230 is normally closed at the bottom of the expansion chamber by a spring loaded relief valve 232 having a small hole 233 therethrough to permit slow leakage of oil from the chamber into the recoil mechanism. If surges are set up in the oil in recoil cylinder 220 by rearward movement of piston 219, some oil will be forced up through the passages 230 whence it will pass into the expansion chamber 50 after having unseated valves 232. At each side of recoil cylinder 220 is a plunger cylinder 234 in each of which is slidably mounted a plunger 235 having within it a portion of the long plunger spring 236 that extends to the rear end of the gun and is prevented from buckling outside the plunger by a guide rod 231 inside the spring. The plunger cylinders are connected to recoil cylinder 22!) by ports 238 that are in communication with the annular groove 239 in cylinder 220, the cut-away portions 240 in the inner face of cylinder 22!] being continuous with groove 239. In the forward end of eachplunger cylinder is a recess 2 that serves as a dash pot to lessen the impact of the carrier against the breech housing when the plungers are returned by springs 236, the pressures in the two dash pots being equalized by a pipe 258 that connects them together. Yoke 242 is connected to both of the plungers 235 at their outer ends and to carrier 219 by a spring pressed-plunger 243 disposed in recess 244 in the carrier, the plunger 243 having a square face 245 to engage the wall of opening 246 in the plunger yoke and being held against rotation in recess 244 by pin 241 that extends into a longitudinal slot in plunger 243. Carrier I I9 is moved back by engagement of the rear edge of yoke 242 against face M9 on the carrier.

As barrel 41 is moved back by the recoil, piston 2l9 is also moved back, being connected to the barrel through piston rod 21 8 and yoke 11. Pressure 'is thus applied to the oil in cylinder 220 back of piston 219 which unseats valve 222 and allows the oil to flow through port 229 into the space forward of the piston, the motion of the piston moving throttling tube 22! over throttling rod 225 and so decreasing the area of the orifice through which the oil flows into the cylinder and checking the recoil. A portion of the oil back of the cylinder may be forced through port 23i, passages 230 and valve 232 into the expansion chamber 50. The cross sectional area of piston rod 2l8 is equal to the combined. cross sectional areas of the plunger cylinders. Thus a quantity of oil sufficient to fill the space left by the rearward movement of the plungers as the plungers are moved through the recoil distance due to their connection to the carrier through the plunger yoke 242 is caused to pass into the plunger cylinders through being displaced by the piston rod. This prevents the sharp blow that would result if the plunger cylinders remained empty until oil is forced into them by forward movement of the piston.

When recoil spring returns the gun to battery, piston 2 I9 is simultaneously moved forwardly and the oil in cylinder 220 in front of the piston is placed under pressure and valve 222 is seated after the piston has traveled a sumcient distance to clear the valve from bolt 226, thus preventing movement of oil through the throttling tube to the rear portion of the cylinder. Piston 2l9 has on its lower forward portion a Passage 248, which decreases in cross section rearwardly, through which the oil passes to annular groove 239'through port 238 to the plunger cylinders, the volume of the plunger cylinders being substantially the same as that part of the volume of the forward portion of cylinder 220 that is not occupied by piston rod 2 i8, when the piston is in its recoil position, and thus the return of piston 2i9 to its forward position forces just enough oil into the plunger cylinders to move the plungers the desired distance. It is apparent that as piston 2l9 moves forward, the space in passage 248 through which the oil may go into groove 239 diminishes and hence there is effected a throttling action that checks the movement of the barrel as it returns to battery. The valve stroke adjusting bolt 226 may be set to hold valve 222 open for any part of the return movement of the piston to entrap the correct quantity of oil in front of the piston to supply the plunger cylinders. If the pressure in front of the piston becomes excessive after the piston has moved forwardly of port 25l, some of the oil will pass from cut-away portion 240, through port 249, unseat valve 256- and pass to the rear portion of the cylinder, back of the piston, through port 251 (Fig. 5).

Forcing the oil from cylinder 22!! into the plunger cylinders drives back the plungers 236 with their connecting yoke 242 and since the yoke is connected to carrier 2i9, the carrier is also moved back which extracts the spent case from. chamber 61, ejects it from the gun and operates the cocking mechanism. When piston 2l9 has reached the forward end of the cylinder, thus uncovering groove 240, the energy stored up in plunger springs 236 drives the carrier forward and rams a loaded cartridge into the chamber, the oil from the plunger cylinders returning to cylinder 22!! through ports 238, annular groove 2 39 and the cut-away portion 240. 

